Method for passing a failsafe alarm signal through a life safety system that experiences a catastrophic failure

ABSTRACT

An improved life safety system provides ability to detect a catastrophic failure within a network node of the life safety system, and to subsequently pass a failsafe alarm signal through a network node, and through the life safety system, despite the catastrophic failure, which may be a failed main processor of a main panel, a failed main processor of a loop expander module, a failed main processor of an amplifier, or a failed main processor of a liquid crystal display controller.

BACKGROUND

1. Field of the Invention

The field of the invention relates to life safety systems generally, andmore particularly to certain new and useful advances in detecting analarm condition and propagating a failsafe alarm signal undercatastrophic failure conditions within a life safety system itself, ofwhich the following is a specification, reference being had to thedrawings accompanying and forming a part of the same.

2. Discussion of Related Art

Life safety systems, including fire detection systems and massnotification systems, include many components, such as fire notificationdevices, mass notification devices, network adapters, amplifiers, andthe like, each of which may include firmware and/or one or moremicroprocessors. Without backup or other failsafe designs, acatastrophic failure within a life safety system can put lives at risk.Examples of a catastrophic failure include, but are not limited to, atleast an inoperable microprocessor, defective firmware, and the like.

A common approach to protecting a microprocessor-based life safetysystem against catastrophic system failure is to include one or moreredundant microprocessors and one or more redundant memory components inthe microprocessor-based life safety system. This approach, thougheffective, is a relatively complex and expensive solution; and theincreased system complexity sometimes actually reduces the reliabilityof the microprocessor-based life safety system. Moreover, this approachdoes not properly address catastrophic failures caused by defectivefirmware. For example, with the primary microprocessor and its redundantmicroprocessor each running the same application firmware, there islittle reason to expect that the redundant microprocessor would producea different result when faced with the same firmware defect(s) as theprimary microprocessor. FIG. 3 is a high level block diagram of aconventional primary processor 301, which includes a core microprocessor304 coupled with a power conditioner 302, a nonvolatile (flash) memory305, a clock 303, and a volatile (ram) memory 306.

Less complex failsafe mechanisms than redundant microprocessors andredundant memories have existed previously, but knowledge and teachingsin the art have heretofore restricted their scope of application to asingle node on a network. The term “network node” is defined below.Examples of such less complex failsafe mechanisms include EST3 and IRC3life safety systems. Although effective at minimizing a node's chancesof experiencing catastrophic failure, these less complex failsafemechanisms do not adequately address how to propagate alarms though alife safety system when one or more network nodes distributed across thelife safety system become inoperable or operate in a defective manner.

What is needed is a relatively simple and inexpensive safeguard thatpermits a life safety system to continue functioning in the event of acatastrophic failure within the life safety system.

SUMMARY

The drawbacks described above are overcome by embodiments of an improvedlife safety system described herein, which includes one or more networknodes in communication with each other via a data bus. Use of the databus permits a failsafe alarm signal to be transmitted across networkconnections and ensures the continued signaling of alarm conditionswithin the life safety system—even when there is a catastrophic failureto one or more subcomponents within the life safety system.

An embodiment of a method of operating a life safety system may includedetecting a catastrophic failure within a network node of a life safetysystem. The method may further include generating a fault signalindicative of the detected catastrophic failure. The method may furtherinclude detecting an alarm condition indicative of a life safetyemergency. The method may further include passing a failsafe alarmsignal through the life safety system despite the detected catastrophicfailure.

An embodiment of a life safety system may include a network node coupledwith a data bus. The network node may include a main processor and asubcomponent. The subcomponent may be configured to detect a failure ofthe main processor, to detect an alarm condition indicative of a lifesafety emergency, and, in response to the alarm condition, to pass afailsafe alarm signal through a network node, and through the lifesafety system, via the data bus despite the detected failure of the mainprocessor.

Other features and advantages of the disclosure will become apparent byreference to the following description taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made briefly to the accompanying drawings, in which:

FIG. 1 is a block diagram of an embodiment of a life safety systemconfigured in accordance with principles of the invention;

FIG. 2 is a block diagram of an exemplary network adapter configured foruse in a the embodiment of the life safety system of FIG. 1;

FIG. 3 is a block diagram of a conventional main processor, which may beused in the embodiment of the life safety system of FIG. 1;

FIG. 4 is a block diagram of the embodiment of the life safety system ofFIG. 1 illustrating fault signaling that occurs when a main processorbecomes inoperable;

FIG. 5 is a block diagram of the embodiment of the life safety system ofFIG. 1 illustrating alarm signaling that occurs when the main processorbecomes inoperable and a remote alarm device, coupled with a secondarydevice loop, signals an alarm condition;

FIG. 6 is a block diagram of the embodiment of the life safety system ofFIG. 1 illustrating alarm signaling that occurs when the main processorbecomes inoperable and a remote panel signals an alarm condition;

FIG. 7 is a block diagram of the embodiment of the life safety system ofFIG. 1 illustrating alarm signaling that occurs when the main processorbecomes inoperable and an alarm device, coupled with a main device loop,signals an alarm condition;

FIG. 8 is a block diagram of the embodiment of the life safety system ofFIG. 1 illustrating alarm signaling that occurs when a main processor ina LCD controller becomes inoperable and an alarm device, coupled withthe main device loop, signals an alarm condition; and

FIG. 9 is a flowchart of an embodiment of a method of operating anembodiment of the life safety system of FIG. 1 in the event of acatastrophic failure within the life safety system.

Like reference characters designate identical or correspondingcomponents and units throughout the several views, which are not toscale unless otherwise indicated.

DETAILED DESCRIPTION

Specific configurations and arrangements of the claimed invention,discussed below with reference to the accompanying drawings, are forillustrative purposes only. Other configurations and arrangements thatare within the purview of a skilled artisan can be made or used withoutdeparting from the spirit and scope of the appended claims. For example,while some embodiments of the invention are herein described withreference to life safety systems, a skilled artisan will recognize thatembodiments of the invention can be implemented in any networked systemhaving two or more nodes, each of which contain at least amicroprocessor, firmware, and/or a microcontroller.

As used herein, an element or function recited in the singular andproceeded with the word “a” or “an” should be understood as notexcluding plural said elements or functions, unless such exclusion isexplicitly recited. Furthermore, references to “one embodiment” of theclaimed invention should not be interpreted as excluding the existenceof additional embodiments that also incorporate the recited features.

Life Safety System

FIGS. 1, 4, 5, 6, 7, 8 provide high-level block diagrams of anembodiment of a life safety system 100, configured in accordance withprinciples of the invention to permit the life safety system 100 tocontinue functioning in the event of a catastrophic failure within anetwork node 170 of the life safety system 100.

Referring primarily to FIG. 1, but also to FIGS. 4, 5, 6, 7, and 8, anembodiment of the life safety system 100 includes a network node 170having one or more expansion modules 110, 120, 130, 602, 702. At leastthe expansion modules 110, 120, 130, and 602 are coupled with a data bus800, which is internal to the network node 170.

Each expansion module 110, 120, 130, 602 includes at least a mainprocessor. Each expansion module 110, 120, 130, 602 may also include asubcomponent. For example, the expansion module 110 illustrativelyincludes a main processor 301, coupled with one or more subcomponents102, 202, 104, 106, and 206 that are each coupled with the data bus 800.Although the connection is not shown, a microcontroller 214 of theexpansion module 110 may also be coupled with the data bus 800 inanother embodiment.

The expansion module 120 illustratively includes a main processor 401,coupled with one or more subcomponents 108 and 208, which are eachcoupled with the data bus 800. Each of the one or more subcomponents108, 208 may be configured to detect a failure of the main processor 401and to detect an alarm condition indicative of a life safety emergency.The expansion module 130 illustratively includes a main processor 501.

The expansion module 602 illustratively includes a main processor 601and a microcontroller 612. The microcontroller 612 may be coupled withthe data bus 800.

The network adapter 170 may further include an expansion module 702,which includes a microcontroller 712.

Each of the subcomponents 102, 202, 104, 106, 206, 108, 208 describedabove may be configured to detect a failure of any main processor 301,401, 501, or 601; and to detect an alarm condition indicative of a lifesafety emergency. Each of the subcomponents 102, 202, 104, 106, 206,108, 208 may be further configured to pass a failsafe alarm signal(“1002” in FIGS. 5, 6, 7, and 8) through the network node 170 via thedata bus 800 in response to the detected alarm condition, despite thedetected failure of the main processor 301, 401, 501, or 601.

Although only one network node 170 is illustrated in the Figures, anembodiment of the life safety system 100 may include a plurality ofnetwork nodes. For example, one or more network nodes, configured thesame as, or similar to, the network node 170 may be located at remoteportions of the network media 101, 201, at remote portions of the relaycontacts 103, at remote portions of the device loops 105, 205, and atremote portions of secondary device loops 107, 207.

Network Node

Still referring to FIGS. 1, 4, 5, 6, 7, and 8, a more detaileddescription of the one or more expansion modules 110, 120, 130, 602, 702included in each network node 170 is now provided. For example, in oneembodiment, the expansion modules 110, 120, 130, 602, 702 may include amain panel 110, a loop expander module 120, an amplifier 130, a liquidcrystal display (“LCD”) controller 602, and a light emitting diode(“LED”)/Switch adapter 702. The LCD controller 602 may be coupled with aliquid crystal display 603.

The main panel 110 includes the main processor 301, the microcontroller214, and the subcomponents 102, 202, 104, 106, and 206 mentioned above.Examples of the subcomponents of the main panel 110 include, but are notlimited to: network adapters 102, 202, a common relay 104, and loopadapters 106, 206. The network adapter 102 includes a microcontroller112, and is coupled to the network media 101. The network adapter 202includes a microcontroller 212, and is coupled to the network media 201.The common relay 104 includes a microcontroller 114, and is coupled tothe relay contacts 103.

The loop adapter 106 includes a microcontroller 116, and is coupled tothe device loop 105. The loop adapter 206 includes a microcontroller116, and is coupled to the device loop 205. The device loop 105 and thedevice loop 205 may contain several hundred devices each. The main panel110 further includes a microcontroller 214 coupled with the NAC/Sounder203.

An embodiment of a network adapter 102 is shown in the block diagram ofFIG. 2. As shown in FIG. 2, the network adapter 102 includes amicrocontroller 112 coupled with a transceiver 140, which is coupledwith the network media 101. Optionally, a waveform generator 150 iscoupled with both the microcontroller 113 and the transceiver 140. Themicrocontroller 112 is configured to manage the operation of thetransceiver 140, and may optionally be configured to manage theoperation of the waveform generator 150. Although not shown in FIG. 2,the network adapter 202 (of FIG. 1) includes the same components and beconfigured the same as the network adapter 102.

In an embodiment, the network adapters 102, 202 are an integral part ofa failsafe communication link, because they are configured to detect analarm condition (1001, 1101, 1201 in FIGS. 5, 6, 7, and 8) indicative ofa life safety emergency, and to send a failsafe alarm signal (1002 inFIGS. 5, 6, 7, and 8) across the network media 101,201 that can berecognized by another network adapter on the other side of the networkmedia 101,201.

Referring again to FIGS. 1, 4, 5, 6, 7, and 8, the loop expander module120 includes its own main processor 401 and the subcomponents 108, 208mentioned above. Examples of the subcomponents of the loop expandermodule 120 include, but are not limited to, the additional loop adapters108 and 208. The loop adapter 108 includes a microcontroller 118, and iscoupled with a secondary device loop 107. The loop adapter 208 includesa microcontroller 218, and is coupled with a secondary device loop 207.Each of the secondary device loops 107 and 207 may include severalhundred devices each.

Another example of an expansion panel that may be included within anetwork node 170, the amplifier 130 includes its own main processor 501,and is configured to amplify a fault signal (“901” in FIG. 4) and afailsafe alarm signal (“1002” in FIGS. 5, 6, 7, and 8) passing throughthe life safety system 100 over the data bus 800. The amplifier 130 iscoupled with a speaker circuit 209.

Another example of an expansion panel that may be included within anetwork node 170, the LCD controller 602 includes its own main processor601 and a microcontroller 612. Although the connection is not shown, themicrocontroller 612 may be coupled with the data bus 800 in oneembodiment.

Another example of an expansion panel that may be included within anetwork node 170, the LED/Switch adapter 702 includes a microcontroller712.

Data Bus

In an embodiment, the expansion panels 110, 120, 130, 602 arecommunicatively coupled via the data bus 800 mentioned above. Inparticular, the data bus 800 couples the main panel 110 with the loopexpander module 120, couples the loop expander module 120 with theamplifier 130, and couples the amplifier 130 with the LCD controller602. In an embodiment, the data bus 800 is part of a single failsafecommunication link provided within each network node 170 of the lifesafety system 100 that allows an alarm condition to be signaledinternally in the event of a catastrophic failure within the life safetysystem 100.

In one embodiment, the data bus 800 is placed in a logic high stateduring normal operation of the network node 170. To pass a failsafealarm signal (1002 in FIG. 5) through the network node 170, and throughthe life safety system 100, a subcomponent 102, 202, 104, 106, 206, 108,208 (or a microcontroller 214, 612) of the network node 170 isconfigured to pull the data bus 800 low when both a failure of a mainprocessor 301, 401, 501, or 601 and an alarm condition indicative of alife safety emergency are detected. As further explained below,detecting the alarm condition may include receiving an alarm signal froman expansion panel of a remote network node (not shown) or receiving analarm signal from a remote alarm device.

FIG. 4 is a block diagram of the embodiment of the life safety system100 of FIG. 1 illustrating fault signaling 901 that occurs when a mainprocessor 301 in the main panel 110 becomes inoperable (e.g., suffers acatastrophic failure). The fault condition is relayed over the data bus800 as the fault signal 901 to various components of the network node170, and to one or more remote components of the life safety system 100,even though the main processor 301 has failed.

For example, when the main processor 301 fails, one or more remotepanels (not shown) that form part of the network media 101, 201 maydetect the microprocessor failure and signal 901 the fault conditionthrough out each of the expansion modules 110, 120, 130, and 602. Forexample, the fault condition may be signaled 901 on a relay troublecontact 141, of the relay contacts 103; and signaled 901, via the LCDcontroller 602, on a user interface in the form of visible, audible, andtext indications. The user interface may be displayed on a liquidcrystal display 603 operated by the LCD controller 602.

FIG. 5 is a block diagram of the embodiment of the life safety system100 of FIG. 1 illustrating alarm signaling 1001, 1002 that occurs whenthe main processor 301 of the main panel 110 becomes inoperable and aremote alarm device 1003, coupled with a secondary device loop 207,activates to generate and transmit an alarm signal 1001 to the expansionmodule 110.

Referring to FIG. 5, subsequent to a failure of the main processor 301,the alarm device 1003, on the secondary device loop 207, may generateand transmit the alarm signal 1001, which indicates the existence of alife safety emergency, such as a fire. When this occurs, a failsafealarm signal 1002 will be generated by the microcontroller 218 of theloop adapter 208 and propagated through network node 170, and throughthe life safety system 100, over the data bus 800.

In one embodiment, the failsafe alarm signal 1002 causes outputs on thesecondary device loop 107 and outputs on the device loops 105, 205 to beactivated; causes outputs on an alarm relay 151 and outputs on a speakercircuit 209 to be activated; causes outputs for the NAC/sounder 203 tobe activated; and causes outputs for the network media 101, 201 to beactivated. Additionally, the failsafe alarm signal 1002 causes afailsafe alarm condition to be annunciated on a user interface displayedon a liquid crystal display 603, which is controlled by the LCDcontroller 602. This operation is the same when the LCD controller 602is configured as a repeater/remote annunciator.

In an embodiment, the failsafe alarm signaling 1002 across the lifesafety system 100 is bi-directional. For example, the failsafe alarmsignal 1002 can originate on a network node, such as main panel 110,that has a failed subcomponent, such as main processor 301.Alternatively, the failsafe signal 1002 can originate elsewhere withinthe life safety system 100 and be propagated to, and through, any failednetwork node. The form of the failsafe alarm signal 1002 depends on thetechnology of the network connection(s). For a DSL or RS485 networkconnection, the failsafe alarm signal 1002 may be an analog signal inthe about 400 Hz to about 4,000 Hz frequency range.

In an embodiment, the loop expander module 120 will have full knowledgeof the outputs and sounders to control its secondary device loops 107,207 via stored programming. Other outputs in the network node 170, andin the life safety system 100, may default to common alarm protocols.

FIG. 6 is a block diagram of the embodiment of the life safety system100 of FIG. 1 illustrating alarm signaling 1101, 1002 that occurs whenthe main processor 301 becomes inoperable and a remote expansion panel1103 in network media 201 activates to generate and transmit an alarmsignal 1101, which indicates the existence of a life safety emergency.When this occurs, the failsafe alarm signal 1002 may be generated by themicrocontroller 212 of the network adapter 202 and thereafter propagatedthrough the life safety system 100 as described above with reference toFIG. 5. For example, subsequent to the failure of the main processor301, the network adapter 202 will sense an alarm signal 1101 generatedby the remote expansion panel 1103 and will generate the failsafe alarmsignal 1002 back to the remote expansion panel 1103. In effect, this issimilar to a local alarm activation under normal operating conditions.The network adapter 202 will also pass the failsafe alarm signal 1002through the main panel 110 that has failed to the rest of the lifesafety system 100. This “pass-through” capability of the failsafe alarmsignal 1002 is active even if the network adapters 102, 202 areconfigured for different media—for example, RS485 to single mode fiber.

FIG. 7 is a block diagram of the embodiment of the life safety system100 of FIG. 1 illustrating alarm signaling 1201, 1002 that occurs whenthe main processor 301 becomes inoperable and an alarm device 1203,coupled with a device loop 205, activates to generate and transmit analarm signal 1201, which indicates the existence of a life safetyemergency. When this occurs, the failsafe alarm signal 1002 may begenerated by the microcontroller 216 of the loop adapter 208 andthereafter propagated through the life safety system 100 as describedabove with reference to FIG. 5. FIG. 7 further illustrates that when analarm device 1203 activates, even the failure of the main processor 301does not lose or drop an alarm signal 1201. The alarm device 1203 willmake the decision to alarm, and because the microcontroller 216 on theloop adapter 208 will detect the alarm condition and assert the failsafealarm signal 1002. Thus, all alarm devices 1203 are still capable ofsignaling an alarm even in the event a catastrophic failure within thelife safety system 100.

FIG. 8 is a block diagram of the embodiment of the life safety system100 of FIG. 1 illustrating alarm signaling that occurs when a mainprocessor 601 in a LCD controller 602 becomes inoperable and an alarmdevice 1203, coupled with the device loop 205, activates to generate andtransmit an alarm signal 1201, which indicates the existence of a lifesafety emergency. When this occurs, the failsafe alarm signal 1002 maybe generated by the microcontroller 216 of the loop adapter 208 andthereafter propagated through the life safety system 100 as describedabove with reference to FIG. 5. FIG. 8 further illustrates that if themain processor 601, which controls a user interface (not shown), fails,then the visible, audible, and text fault indications will indicatefailure. In an embodiment, this may include blinking or blanking theliquid crystal display 603, which is controlled by the LCD controller602.

FIG. 9 is a flowchart illustrating functions of an embodiment of amethod 1400 of operating an embodiment of a life safety system 100.Unless otherwise indicated, the functions of the method, represented byfunctional blocks 1401, 1402, 1403, 1404, 1405, 1406, and 1407 may beperformed sequentially, simultaneously, or in any suitable order.Referring to FIGS. 1 and 9, as represented by functional block 1401, themethod 1400 includes detecting a catastrophic failure within a lifesafety system 100. As represented by functional block 1402, the functionof detecting a catastrophic failure includes detecting a failure of amain processor 301, 401, 501, 601 in a network node 170 of a life safetysystem 100. As represented by functional block 1403, the method 1400further includes generating a fault signal indicative of the detectedcatastrophic failure. The fault signal may be any of the fault signals901 in FIG. 4. As represented by functional block 1404, the method 1400further includes detecting an alarm condition indicative of a lifesafety emergency. The alarm signal may be any of the alarm signals 1001,1101, or 1201 of FIGS. 5, 6, 7, and 8. As represented by functionalblock 1405, the method 1400 further includes generating and passing afailsafe alarm signal through the life safety system 100 in spite of thedetected catastrophic failure. The failsafe alarm signal may be thefailsafe alarm signal 1002 in FIGS. 5, 6, 7, and 8. As represented byfunctional block 1406, the function of passing a failsafe alarm signalthrough the life safety system 100 may further include annunciating atleast one of visual, textual, and audible indications on a userinterface of a liquid crystal display 603, which is controlled by theLCD controller 602. As represented by functional block 1407, thefunction of asserting a failsafe alarm signal may further includeblinking or blanking a liquid crystal display 603.

Each block, or combination of blocks, depicted in the flowchart of FIG.9 can be implemented by computer program instructions. These computerprogram instructions may be loaded onto, or otherwise executable by, acomputer processor, such as the main processor 301, 401, 501, or 601 orother programmable apparatus, such as any of microcontrollers 112, 114,116, 118, 214, 216, 218, 612 to produce a machine, such that theinstructions which execute on the computer processor or otherprogrammable apparatus create means or devices for implementing thefunctions specified in the flowchart of FIG. 9. These computer programinstructions may also be stored in a computer-readable memory that candirect the computer processor or other programmable apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture,including instruction means or devices which implement the functionsspecified in the block diagrams of FIGS. 1, 2, 4, 5, 6, 7, and 8, and inthe flowchart of FIG. 9.

There is an economic advantage and a reliability advantage of using thesimplified embodiment of the life safety system 100 described herein ascompared to using the complex redundant microprocessor implementationpreviously in use. Moreover, without the implementation of a failsafealarm signaling method and system as herein described, the capacity ofredundant microprocessor based systems is limited by European codes andstandards. Advantages of economies of scale can be realized once anembodiment of the failsafe alarm signaling method and system isimplemented.

Embodiments of the invention herein described and claimed may provideone or more technical effects. With reference to FIGS. 5, 6, 7, and 8,one technical effect is passing a failsafe alarm signal 1002, via a databus 800, through one or more expansion modules 110, 120, 130, 602 of anetwork node 170, and through the life safety system 100, despite one ormore failed main processors 301, 401, 501, 601. Use of the data bus 800is opposite prior teachings in the art to use complex architecture thatrequires redundant microprocessors.

Although specific features of various embodiments of the invention maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the invention, the feature(s)of one drawing may be combined with any or all of the features in any ofthe other drawings. The words “including”, “comprising”, “having”, and“with” as used herein are to be interpreted broadly and comprehensivelyand are not limited to any physical interconnection. Moreover, anyembodiments disclosed herein are not to be interpreted as the onlypossible embodiments. Rather, modifications and other embodiments areintended to be included within the scope of the appended claims.

1. A method, comprising: detecting a catastrophic failure within anetwork node of a life safety system; generating a fault signalindicative of the detected catastrophic failure; detecting an alarmcondition indicative of a life safety emergency; and passing a failsafealarm signal through the network node despite the detected catastrophicfailure.
 2. A method in accordance with claim 1, wherein the detecting acatastrophic failure further comprises: detecting a failure of a mainprocessor.
 3. A method in accordance with claim 1, wherein the passing afailsafe alarm signal through the network node further comprises:annunciating at least one of visual, textual, and audible indications ona user interface of a liquid crystal display.
 4. A method in accordancewith claim 3, wherein the annunciating at least one of visual, textual,and audible indications further comprises: one of blinking and blankingthe liquid crystal display.
 5. A life safety system, comprising: anetwork node including one or more expansion panels communicativelycoupled with a data bus, wherein each of the one or more expansionpanels includes a main processor and a subcomponent, and wherein thesubcomponent is configured to detect a failure of the main processor, todetect an alarm condition indicative of a life safety emergency, and, inresponse to the alarm condition, to pass a failsafe alarm signal throughthe network node via the data bus despite the detected failure of themain processor.
 6. A life safety system in accordance with claim 5,wherein the subcomponent is configured to pull the data bus low when thefailure of the main processor is detected, and an alarm conditionindicative of a life safety emergency has also been detected.
 7. A lifesafety system in accordance with claim 5, wherein network node includesa main panel coupled with the data bus.
 8. A life safety system inaccordance with claim 7, wherein the subcomponent is a network adapterincluded in the main panel.
 9. A life safety system in accordance withclaim 5, wherein the network node includes a loop expander modulecoupled with the data bus.
 10. A life safety system in accordance withclaim 9, wherein the subcomponent is a loop adapter included in the loopexpander module.
 11. A life safety system in accordance with claim 5,wherein the network node includes an amplifier coupled with the databus.
 12. A life safety system in accordance with claim 5, wherein thenetwork node includes a liquid crystal display controller coupled withthe data bus.